Effects of varying blood flow rate during peripheral veno-arterial extracorporeal membrane oxygen (V-A ECMO) on left ventricular function measured by two-dimensional strain.

Background: We evaluated the effects of varying blood flow rate during peripheral veno-arterial extracorporeal membrane oxygen (V-A ECMO) on left ventricular function measured by two-dimensional strain. Methods: Adult patients who were supported by peripheral V-A ECMO were recruited. Serial hemodynamic and cardiac performance parameters were measured by transthoracic echocardiogram within the first 48 h after implementation of V-A ECMO. Measurements at 100%, 120%, and 50% of target blood flow (TBF) were compared. Results: A total of 54 patients were included and the main indications for V-A ECMO were myocardial infarction [32 (59.3%)] and myocarditis [6 (11.1%)]. With extracorporeal blood flow at 50% compared with 100% TBF, the mean arterial pressure was lower [66 ± 19 vs. 75 ± 18 mmHg, p < 0.001], stroke volume was greater [23 (12-34) vs. 15 (8-26) ml, p < 0.001], and cardiac index was higher [1.2 (0.7-1.7) vs. 0.8 (0.5-1.3) L/min/m2, p < 0.001]. Left ventricular contractile function measured by global longitudinal strain improved at 50% compared with 100% TBF [-2.8 (-7.6- -0.1) vs. -1.2 (-5.2-0) %, p < 0.001]. Similarly, left ventricular ejection fraction increased [24.4 (15.8-35.5) vs. 16.7 (10.0-28.5) %, p < 0.001] and left ventricular outflow tract velocity time integral increased [7.7 (3.8-11.4) vs. 4.8 (2.5-8.5) cm, p < 0.001]. Adding echocardiographic parameters of left ventricular systolic function to the Survival After Veno-arterial ECMO (SAVE) score had better discriminatory value in predicting eventual hospital mortality (AUROC 0.69, 95% CI 0.55-0.84, p = 0.008) and successful weaning from V-A ECMO (AUROC 0.68, 95% CI 0.53-0.83, p = 0.017). Conclusion: In the initial period of V-A ECMO support, measures of left ventricular function including left ventricular ejection fraction and global longitudinal strain were inversely related to ECMO blood flow rate. Understanding the heart-ECMO interaction is vital to interpretation of echocardiographic measures of the left ventricle while on ECMO.

Sensitivity of ventricular systolic function to afterload during veno-arterial extracorporeal membrane oxygenation.

AIMS: Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) increases afterload to the injured heart and may hinder myocardial recovery. We aimed to compare the sensitivity of left ventricular (LV) systolic function to the afterload effects of peripheral V-A ECMO during the acute and delayed stages of acute myocardial dysfunction. METHODS AND RESULTS: A total of 46 adult patients who were supported by peripheral V-A ECMO between April 2019 and June 2021 were analysed. Serial cardiac performance parameters were measured by transthoracic echocardiography (TTE) on mean day 1 ± 1 of V-A ECMO initiation (n = 45, 'acute phase') and mean day 4 ± 2 of V-A ECMO initiation (n = 36, 'delayed phase'). Measurements were obtained at 100%, 120%, and 50% of ECMO target blood flow (TBF). LV global longitudinal strain (GLS) significantly improved from -6.1 (-8.9 to -4.0)% during 120% TBF to -8.8 (-11.5 to -6.0)% during 50% TBF (P < 0.001). The sensitivity of LV GLS to changes in ECMO flow was significantly greater in the acute phase of myocardial injury compared with the delayed phase [median (IQR) percentage change: 72.7 (26.8-100.0)% vs. 22.5 (14.9-43.8)%, P < 0.001]. Findings from other echocardiographic parameters including LV ejection fraction [43.0 (29.1-56.8)% vs. 22.8 (9.2-42.2)%, P = 0.012] and LV outflow tract velocity-time integral [45.8 (18.6-58.7)% vs. 24.2 (12.6-34.0)%, P = 0.001] were similar. A total of 24 (52.2%) patients were weaned off ECMO successfully. CONCLUSIONS: We demonstrated that LV systolic function was significantly more sensitive to the afterload effects of V-A ECMO during the acute stage of myocardial dysfunction compared with the delayed phase. Understanding the evolution of the heart-ECMO interaction over the course of acute myocardial dysfunction informs the clinical utility of echocardiographic assessment in patients on V-A ECMO.

Respiratory arrest requiring resuscitation as a rare presentation of obstructive sleep apnoea and hypothyroidism.

A 79-year-old man, who had significant cardiovascular morbidities, presented with out-of-hospital respiratory arrest. He regained breathing after brief cardiopulmonary resuscitation by his paramedic son. After meticulous investigations, acute cardiovascular events and metabolic causes were ruled out while features of obstructive sleep apnoea were elicited. The findings on in-laboratory polysomnography were compatible with severe obstructive sleep apnoea, with unusually prolonged apnoea duration of up to 2.7 min which most likely accounts for the presentation as 'respiratory arrest'. Thyroid function test for investigation of his weight gain confirmed hypothyroidism. His symptoms improved gradually after positive airway pressure therapy with bi-level support and thyroxine replacement. On further evaluation, his hypothyroidism is believed to be a complication of long-term amiodarone exposure. The case highlights that the combination of obstructive sleep apnoea and hypothyroidism can lead to catastrophic manifestation and the unusually long apnoea could be a feature prompting further workup for possible hypothyroidism.